The invention relates to electrical switching and/or other electrical parameter changing by a mechanical translating element, particularly suitable for piano action keyboard for electronic musical instruments, characterized by a sensitive touch response or feel and practicality of high volume manufacture and utilization, having regard to considerations of reliability, effectiveness and cost.
It is a principal object of the invention to provide an electrical switching and/or other electrical parameter changing mechanism suitable for use in electronic musical instrument piano keyboard action described in the copending U.S. patent application of P. V. W. Dodds, Ser. No. 000,588, filed Jan. 2, 1979, now U.S. Pat. No. 4,217,803 granted Sept. 10, 1980, of common assignment with this application, and the disclosure of which including--background, objects, summary, drawing, description and claims--is incorporated herein by reference as though set out at length herein.
It is a further object of the invention to provide a switching and/or other electrical parameter changing mechanism assuring reliable contact with low actuating force applied by the mechanism and reliable contact break upon removal of the actuating force, to enable usability with a sensitive feel of the force applying linkage of the mechanism as described in said copending application consistent with the preceding object.
It is a further object of the invention to consistently apply a stable level (approximate) of actuating force and low dynamic friction consistently with one or more of the preceding objects and in the context thereof or in equivalent contexts.
As used hereinafter (unless otherwise stated), "electrical switching" refers broadly to electrical circuit making or breaking by closing or opening contacts and also to other forms of change in electrical circuits or electrical circuit analogues such as electromagnetic or magnetic pickups, Hall effect pickups, electrostatic pickups, capacitive pickups, rheostats, potentiometers or the like which can be used to make or break electric (or other) circuits or change a parameter thereof.
In accordance with the present invention, electrical switching is accomplished through use of multiple elongated electrical switching elements such as those of the elastomeric membrane type. Membrane type key switches are known for their low cost, consistent with reliability and have been utilized in touch-type keyboards for calculators and kitchen appliances. They typically have a conductive pattern on a board overlaid with a polyester film containing holes which is in turn overlaid by a conductive resilient sheet which can be pressed to penetrate under pressure and make contact with that portion of the conductive pattern underneath. Thus the switching element presents an elongated compliant surface (of the top elastomeric film). Finger and key pressures have been used to activate the compliance surface by pushing it down and therefore causing the conductive pattern underneath it to make contact with the basic conductive pattern on the board. In accordance with the present invention, providing an effective coupling with a piano action activating mechanism is practically accomplished through use of a resilient spring arm mounted on an end of the mechanism which is selectively moveable parallel to the elongated compliant surface and in turn mounting a roller element (spherical, cylindrical or other effective roller forms) on the spring end to maintain continuous contact with the elongated compliant surface with a force against the surface of 1-5 ozs., preferably 2 ozs., the force being established by the configuration of the spring transmitting activating force from the moving mechanism.